© 2004 Heron Publishing—Victoria, Canada
Functional relationships between crown morphology and within-crown characteristics of understory saplings of three codominant
conifers in a subalpine forest in central Japan
Akira Mori (1, 2) and Hiroshi Takeda (1)
1. Laboratory of Forest Ecology, Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University,
Oiwake-Cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan / 2. Corresponding author (akkym@kb3.so-net.ne.jp) / Received August 8, 2003; accepted October 19, 2003; published online April 1, 2004
Summary
Light-related plasticity of crown morphology and within-crown characteristics were investigated in understory sun and shade
saplings of three codominant subalpine conifers, Abies mariesii M.T. Mast., Abies veitchii Lindl. and Picea jezoensis var. hondoensis (Mayr) Rehd. Compared with those of sun saplings, current-year shoots of shade saplings allocated less biomass to needles,
resulting in less dense needle packing and hence less mutual needle shading. The proportion of lateral branch biomass in foliage
was either similar in sun and shade saplings or greater in shade saplings, depending on the species, suggesting that, over
the lifetime of a branch, greater needle longevity in shade compensates for reduced biomass investment in needles of current-year
shoots of shade saplings. Saplings with slower-growing branches tended to have greater needle life spans, suggesting that
plasticity of branch growth rate and plasticity of needle life span are interdependent. Both Abies species showed greater light-related plasticity of needle life span and branch growth than P. jezoensis. The greater shade tolerance of the Abies species derives from their broad flattened crowns with slow-growing branches. This type of crown development incurs substantial
support costs, but the long needle life span of shade saplings of the Abies species compensates, at least in part, for their low annual investment in foliage, especially in the case of A. mariesii, which has a longer needle life span and slower-growing and stouter branches than A. veitchii. Compared with the Abies species, P. jezoensis had a less plastic crown morphology, and less variability of needle life span and branch growth in response to light, resulting
in lower shade tolerance. However, compared with the flattened crown of Abies shade saplings, the conical crown of P. jezoensis saplings imposes a smaller support cost, making this species better adapted to rapid height growth than to survival in shade.
Keywords:
Abies mariesii, Abies veitchii, allocation, branch growth, light regime, needle life span, Picea jezoensis var. hondoensis, plasticity.
